The present invention relates to a fuel injection apparatus for internal combustion engines of the type having fuel injection valves or injectors. Fuel injection systems typically comprise a plurality of injectors connected to a fuel carrying conduit from a fuel reservoir by means of a pump. The injectors may be connected to the fuel carrying conduit directly or they may be connected by separate fuel lines. The injectors may be of the commonly known type of electromagnetic injector wherein each injector functions as a metering valve permitting a determinable amount of fuel to enter into the engine. Alternatively, the injectors may be of the type which open automatically when the pressure immediate the injector achieves a prescribed threshold. This latter type of valve performs no metering function. Metering is obtained by a mechanical or electrical centering valve. These pressure responsive injector valves are typically found in compression ignition diesel engines operating between pressures of 4500 psi and 10,000 psi or as may be found in a low pressure spark ignition engine wherein the valve may automatically open when the pressure approximate the valve reaches a pressure between 60 and 80 psi. The use of a single central metering valve in a multipoint fuel injection system has been disclosed by Monpetit et al. in U.S. Pat. No. 3,728,984 which issued on Apr. 24, 1973.
One of the problems identified with previously disclosed fuel distribution systems of this type is the fact that a non-negligible amount of fuel is trapped in the fuel lines connecting the injectors to the central metering valve. A consequence of this entrapped fuel can be seen from the following. During sustained engine operation the engine will invariably attain a relatively high operating temperature. When the engine is shut off the entrapped fuel will have a tendency to vaporize. This vaporization deteriorates the engine's performance during subsequent starts. The present invention obviates these problems.
According to the specific embodiment of the invention illustrated in the drawings of this application and discussed in detail below, the present invention supplies a determinable quantity of fuel to at least one of a plurality of fuel injection valves or injectors. The invention comprises a check valve metering system interconnecting a constant flow pump and fuel rail having at least one injector. The check valve metering system further comprising a bi-level pressure means including a series combination of two pressure regulators having an input end, a common node and output end. The input end is maintained in fluid communication with a fuel supply while the output end is in fluid communication with a return conduit to bring excess fluid back to the fuel supply. The input end and common node are in fluid communication with a series combination of two ports of a 3-way valve, fuel rail and check valve. A third port of the 3-way valve is selectively maintained in fluid communication with a second return conduit having a restriction such as an orifice. The second return conduit is connected in common to the return conduit and to the output of the bi-level pressure means. In accordance with teachings of the present invention the direction of flow through the fuel rail is determined by selectively porting the 3-way valve to the fuel rail or to the second return conduit in response to control signals input thereto. According to one aspect of the invention the fuel system can be operated in a fuel recirculating mode during periods of non-injection and in a reverse flow dead ended mode during periods involving fuel injection.
An advantage of the present invention is that rapid response is achieved by virtue of the independently selectable levels of regulated pressure. A further advantage of the present invention is that accurate fuel metering is achieved by virtue of the systems rapid response characteristics, the dead-ended configuration during injection, and the independently electrically actuated 3-way valve.
An object of the present invention is to meter fuel accurately. Another object of the present invention is to design a central metering injection system having a circulating fuel flow to the injectors which will retain the advantages of the central metering approach.
A further object of the present invention is to minimize performance variations resulting from fuel vaporization and air bubbles carried by the fuel.
Many other objects and purposes of the invention will be clear from the following description of the drawings.